Methods and organisms for concentrating and recovering metals and minerals from aqueous media

ABSTRACT

The present invention relates to methods and organisms for concentrating and recovering metals and minerals from aqueous media. In the inventive method, a eucaryotic aquatic organism capable of concentrating a metal or mineral is contacted an aqueous medium containing the metal or mineral, in order to concentrate the metal or mineral in the organism. Following concentration, the metal or mineral accumulated by the organism may be recovered. Sponges are very preferable organisms for isolating metals, e.g, gold and silver, from seawater.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to methods and organisms forconcentrating and recovering metals and minerals from aqueous media.

[0003] 2. Discussion of the Background

[0004] It is well-recognized that the oceans, lakes, and streams of theworld contain significant quantities of metals, including rare, preciousand strategic metals, e.g., gold. However, methods of economicallyextracting such metals are lacking.

[0005] The recovery of common minerals that are dissolved in seawaterhas been conducted for several centuries. It is economically feasible toextract materials contained at sufficiently high concentrations inseawater, such as salt, manganese and bromine. However, the morevaluable minerals, e.g., gold, silver and platinum, exist in such smallconcentrations that extraction by current commercial means is morecostly than can be justified by the value of the recovered metals.

[0006] In the last hundred years, many efforts have been made to developefficient means of recovering these valuable metals from aqueous media.Such efforts have included chemical precipitation, resin gel filtration,etc. Many of these techniques were technically successful, but all wereeconomically impractical since the cost of reagents, equipment, andenergy exceeded the value of the recovered materials.

[0007] To be economically viable, the equipment for recovering metalsand minerals from aqueous media must be extremely cheap to produce andmaintain, and must be capable of processing relatively large volumes ofwater at a very low cost.

SUMMARY OF THE INVENTION

[0008] The present invention is directed to methods of economicallyextracting metals and minerals from an aqueous environment using aquaticorganisms which are capable of removing metals and/or minerals fromwater and storing them in their tissues, i.e., concentrating metalsand/or minerals, and then recovering the metals and/or minerals from theorganisms.

[0009] Accordingly, it is an object of the present invention to providemethods of concentrating metals and minerals from aqueous media. It isanother object of the present invention to provide aquatic organismswhich are capable of concentrating metals and minerals from an aqueousmedium.

[0010] The objects of the invention may be accomplished with a method ofrecovering metals and minerals from aqueous media by contacting anaqueous medium comprising at least one metal or mineral with aeucaryotic aquatic organism capable of concentrating the metal ormineral, to concentrate the metal or mineral in the organism; and thenrecovering the concentrated metal or mineral from the organism.

[0011] The objects of the invention may also be accomplished with atransgenic eucaryotic aquatic organism which is capable of concentratingat least one metal or mineral from an aqueous medium and expresses atleast one heterologous gene which encodes a protein that effects theconcentration of the metal or mineral in the organism.

[0012] The objects of the invention may also be accomplished with atransgenic eucaryotic aquatic organism which is capable of concentratingat least one metal or mineral from an aqueous medium, expresses at leastone heterologous gene which encodes a protein that effects theconcentration of the metal or mineral in the organism, and harbors amicroorganism that is capable of concentrating the metal or mineral froman aqueous medium.

[0013] A more complete appreciation of the invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription.

DETAILED DESCRIPTION OF THE INVENTION

[0014] A wide variety of aquatic organisms may be used in the presentinvention. As used herein, the term “aquatic organism” refers to anorganism which is capable of living in an aqueous environment, such asan ocean, a bay, a lake, a river, wastewater, etc. Preferably, theaquatic organism is an invertebrate species. Examples of suitableinvertebrates include, for example, sponges, mollusks, tube worms,marine annelids, and polyps.

[0015] Sponges are particularly preferred since this organism has theability to process relatively large volumes of water per unit mass.Sponges can filter water at a rate of ten times their own volume perminute. The regenerative properties of sponges are also attractive.Sponges can regenerate completely from very small pieces of the originalorganism. In addition, the feeding and respiration mechanisms of spongesmake them particularly suited for the present invention in terms ofeconomics. Sponges draw in not only the water, but also particulatematter which is used as food. It should be noted that the ingestion ofmicroorganisms and organic matter by the sponges is particularlyimportant for collecting metals, since a large percentage of metals inwater will be associated with the surfaces of the ingested matter. Thein-current openings of sponges are actively cleared of any obstructionsin the normal course of their functioning, making the sponge aself-cleaning “filter”. As the sponges would also tend to reproduce andcreate new sponges, sterile sponges are preferred. The techniques foraccomplishing this have been developed and documented.

[0016] The eucaryotic aquatic organism, e.g., an invertebrate,especially a sponge, may harbor a procaryotic organism (microorganism)which is capable of concentrating metals or minerals from aqueous media.This is a major advantage of the present invention in that themicroorganisms do not have to be bound or attached to a substrate ormatrix in order to control their location. The procaryotic microorganismmay be a bacteria, an algae, or a fungus. Bacteria are preferred.

[0017] In a preferred embodiment, the eucaryotic aquatic organism is atransgenic species which expresses at least one heterologous gene thatencodes a protein which effects concentration of the metal or mineral inthe organism.

[0018] Genes that encode proteins which effect bioaccumulation of metalsand minerals have been identified, isolated, and inserted into otherorganisms. These transgenic organisms have expressed the geneticmaterial and become active bioaccumulators of the target metals. Forexample, the merA gene from soil bacteria is known. This gene has beenmodified (merApe 9) and introduced into Arabidopsis plants (see Claytonet al, Proc. Natl. Acad. Sci., 93, pp.3182-3187, incorporated herein byreference). These genes are also capable of accumulating trivalent goldions. In addition, biochemical pathways that isolate gold are found inseveral existing plants. These pathways isolate dissolved gold andconcentrate it in the plants tissues. An example of a plant that doesthis is the Yugoslavian Horsetail (Gmelin, L., Handbach der AnorgonischeChemie, Vol. 62, pt. 2, 1954). These biochemical pathways are ideallysuited for a marine environment where the concentration of gold in thesurrounding environment is continually replenished.

[0019] The extraction and concentration of metals by organisms(bio-accumulation) is well known, and has received attention byresearchers as a means of cleaning up sites contaminated by heavymetals. Many bacterial have an affinity for these metal ions as part oftheir biochemical cycles. The bio-accumulation of gold by Pedomicrobiumwas described by Watterson in 1991 (see Geology, 20, pp. 315-318, 1991,incorporated herein by reference). Since then, several researchers havereported microbial bio-accumulation of precious metals. These reportsstrongly suggest that the transgenic sponge of the present invention canbe prepared.

[0020] Many marine organisms have symbiotic microorganisms (prokaryotes)of both intracellular and extracellular orientation. The total mass ofthese organisms can equal up to 50% of the host's total weight. Some ofthe symbionts, Cyanobacter for example, are of the same genus asidentified metal bio-accumulators. Organisms containing symbionts aremost sponges, the methane mussel of the Gulf of Mexico, giant tubewormsof the thermal vents, deep sea clams, and most marine invertebrates tosome degree. These symbiotic microorganisms can be geneticallyengineered to bio-accumulate, i.e., concentrate, the desired metal froman aqueous solution.

[0021] In a preferred embodiment, the present invention provides formodifying the symbiotic matrix bacteria indigenous to many spongespecies. These bacteria compose up to 40% of the total mass of somespecies. In this scenario the sponge will provide structural support andgenerate water flow while the bacteria function as active sites for thedesired biochemical processes. These bacteria are passed on fromgeneration to generation in the sponges and are not acquired from thesurrounding environment. In this context, the bacteria cells behave assponge cells. For a discussion of symbiotic microorganisms in sponges,see Preston et al, Proc. Natl. Acad. Sci., 93, pp. 6241-6246,incorporated herein by reference).

[0022] Recent developments in phytoremediation demonstrate that suchmetal-concentrating bacteria can be prepared. A bacterial gene has beenadded to a relative of the mustard plant to create a transgenic plantthat takes up mercury from the soil (Clayton et al, supra). This plantalso transforms the mercury into a less harmful form. Work is under wayto create transgenic plants that target other metals.

[0023] The cell wall precious metal binding sites of some bacteria havebeen identified as teichoic and teichuronic acids (see, for example,Freymond et al, GenBank Accession U13979 and Lazarevic et al, Mol.Microbiol., 16(2), 345-355(1995), both incorporated herein byreference). These are not specific compounds, but rather a class. Eachspecies of microorganism has a structure to these compounds, that isspecific to that species. Bacillus subtilis, a microbe identified asbioactive for osmium, has already had the gene responsible for one ofits teichoic acids sequenced (see Lazarevic et al cited above).

[0024] The following list identifies specific bacteria and the metalsthey are capable of concentrating:

[0025]Bacillus cereus (nucleation of gold crystals)

[0026]Citrobacter intermedius (silver bio-accumulator)

[0027]Acetobacter methanolicus (silver bio-accumulator)

[0028]Thermothrix thiopara (gold and silver bio-accumulator)

[0029] (thermophilic cyanobacteria)

[0030] Phormidium (gold and silver bio-accumulator)

[0031] Oscillatoria (gold and silver bio-accumulator)

[0032] Mastigocladus (gold and silver bio-accumulator)

[0033]Thiobacillus ferrooxidan (silver bio-accumulator)

[0034]Thiobacillus thiooxidans (silver bio-accumulator)

[0035]Bacillus lichenformis (gold bio-accumulator)

[0036] Bacillus BKPM 4368 (bio-accumulation of colloidal and trivalentgold)

[0037] Pedomicrobium (gold and silver bio-accumulator)

[0038]Bacillus subtilis (osmium bio-accumulator).

[0039] The gene(s) responsible for accumulating the metals identifiedabove can be isolated using well-known molecular cloning techniques andinserted into the desired host microorganism. Such routine cloningtechniques are described in, for example, Perbal, A Practical Guide toMolecular Cloning, Second Edition, John Wiley & Sons, 1988 and CurrentProtocols in Molecular Biology, Volumes 1-3, Ausbel et al, Eds., JohnWiley & Sons, 1994-1998, both of which are incorporated herein byreference in their entirety.

[0040] The growth and cultivation of sponges are well-known. For adiscussion of sponge biology, growth and cultivation see, for example,Bergquist, Sponges, University of California Press, 1978; Stevely et al,The Biology and Utilization of Florida's Commercial Sponges, TechnicalPaper No. 8, Technical Paper of the State University System of FloridaSea Grant College Program, University of Florida, Gainesville, October1978; and Stevely et at, Survival and Growth of Cut vs Hooked CommercialSponges in the Florida Keys, Technical Paper No. 38, Florida Sea GrantExtension Program, University of Florida, Gainesville, Project No.IR-82-15, October 1978; all of which are incorporated herein byreference.

[0041] The eucaryotic aquatic organism is contacted with an aqueousmedium containing at least one metal or mineral to be accumulated. Theaqueous medium may be seawater, fresh water from, for example, a riveror a lake. Alternatively, the aqueous medium may be wastewater from anindustrial process. The aqueous medium may also contain variablequantities of organic matter. Seawater is preferred.

[0042] The target metal or mineral may be gold, silver, platinum,osmium, aluminum, scandium, titanium, vanadium, chromium, manganese,iron, cobalt, nickel, copper, zinc, gallium, germanium, arsenic,selenium, strontium, atrium, zirconium, niobium, molybdenum, ruthenium,rhodium, palladium, cadmium, indium, tin, antimony, tellurium, hafnium,tantallum, tungsten, renium, iridium, mercury, thallium, lead, bismuth,or any of the lathanides. The metal is typically in the form of thecation in the aqueous medium. The metal ion may be converted tocorresponding zero-valent metal species in the organism. Gold isespecially preferred for its enormous economic value.

[0043] The aqueous medium and the eucaryotic organism are contacted fora time sufficient to concentrate the metal or mineral in the organism.The contact time may be widely varied. Suitable contact times are fromseveral hours or days to several years, e.g., 1 week to ten years.

[0044] Following concentration of the metal or mineral may be recoveredfrom the organism. For example, the organism may be burned in order toseparate the organic matter form the metal. As used herein, therecovering the metal or mineral from the organism includes recovery fromthe eucaryotic organism, the symbiotic procaryotic organism, or both.

EXAMPLE

[0045] The following is designed to illustrate the implementation of thepresent invention, and is not limiting.

[0046] 2,000,000 sponges can be farmed in a square one thousand yards ona side. The sponges will take four to five years to grow to the averagesize used in our projections (7″ diameter). Consequently, we envisionplanting a sponge bed (or beds) each year for five years. This wouldprovide a steady supply of harvestable sponges after the fifth year.

[0047] The sponges will accumulate gold over their entire life but sincea sponge filters water in proportion to its size, it will accumulatemore than half the total gold collected during its fifth year. Duringthe fifth year each sponge will filter just over a half million cubicfeet of seawater. With two million sponges this is over one trillioncubic feet of water filtered by a sponge bed. This one trillion cubicfeet of ocean water will contain over two million troy ounces of goldthat the sponges will extract from the water and accumulate in theirtissues. The cumulative amount of gold extracted during the five yearperiod should be over 3.8 million troy ounces.

[0048] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A method of recovering metals and minerals from aqueous media,comprising: contacting an aqueous medium comprising at least one metalor mineral an eucaryotic aquatic organism capable of concentrating themetal or mineral, to concentrate the metal or mineral in the organism;and recovering the concentrated metal or mineral from the organism. 2.The method of claim 1 , wherein the aqueous medium is seawater.
 3. Themethod of claim 2 , wherein the metal or mineral is gold.
 4. The methodof claim 1 , wherein the eucaryotic organism harbors a microorganismcapable of concentrating the metal or mineral.
 5. The method of claim 2, wherein the metal or mineral concentrated in the microorganism is alsorecovered.
 6. A method of recovering metals and minerals from aqueousmedia, comprising: contacting an aqueous medium comprising at least onemetal or mineral with an eucaryotic aquatic organism which harbors amicroorganism capable of concentrating the metal or mineral, toconcentrate the metal or mineral in the microorganism; and recoveringthe concentrated metal or mineral from the microorganism.
 7. The methodof claim 6 , wherein the eucaryotic aquatic organism is an invertebrate.8. The method of claim 6 , wherein the invertebrate is selected from thegroup consisting of sponges, mollusks, tube worms, marine annelids andpolyps.
 9. The method of claim 8 , wherein the invertebrate is a sponge.10. The method of claim 9 , wherein the microorganism is a transformedby the insertion of at least one heterologous gene, wherein the gene isexpressed and the expression product is capable of concentrating themetal or mineral in the microorganism.
 11. The method of claim 10 ,wherein the microorganism is a bacteria.
 12. The method of claim 11 ,wherein the aqueous medium is seawater.
 13. The method of claim 12 ,wherein the metal or mineral is gold.
 14. A transgenic eucaryoticaquatic organism which is capable of concentrating at least one metal ormineral from an aqueous medium and expresses at least one heterologousgene which encodes a protein that effects the concentration of the metalor mineral in the organism.
 15. A eucaryotic aquatic organism whichharbors a microorganism that is capable of concentrating at least onemetal or mineral from an aqueous medium.
 16. A transgenic eucaryoticaquatic organism which is capable of concentrating at least one metal ormineral from an aqueous medium, expresses at least one heterologous genewhich encodes a protein that effects the concentration of the metal ormineral in the organism, and harbors a microorganism that is capable ofconcentrating the metal or mineral from an aqueous medium.
 17. A methodof concentrating metals and minerals from aqueous media, comprising:contacting an aqueous medium comprising at least one metal or mineralwith the organism of claim 14 , to concentrate the metal or mineral inthe organism.
 18. A method of concentrating metals and minerals fromaqueous media, comprising: contacting an aqueous medium comprising atleast one metal or mineral with the organism of claim 15 , toconcentrate the metal or mineral in the microorganism.
 19. A method ofconcentrating metals and minerals from aqueous media, comprising:contacting an aqueous medium comprising at least one metal or mineralwith the organism of claim 16 , to concentrate the metal or mineral inthe organism and the microorganism.
 20. A method of recovering metalsand minerals from aqueous media, comprising: contacting an aqueousmedium comprising at least one metal or mineral with the organism ofclaim 14 , to concentrate the metal or mineral in the organism; andrecovering the concentrated metal or mineral from the organism.
 21. Amethod of recovering metals and minerals from aqueous media, comprising:contacting an aqueous medium comprising at least one metal or mineralwith the organism of claim 15 , to concentrate the metal or mineral inthe microorganism; and recovering the concentrated metal or mineral fromthe microorganism.
 22. A method of recovering metals and minerals fromaqueous media, comprising: contacting an aqueous medium comprising atleast one metal or mineral with the organism of claim 16 , toconcentrate the metal or mineral in the organism and the microorganism;and recovering the concentrated metal or mineral from the organism andthe microorganism.